Recently, I filled the tank of my '99 E430 and noticed that the gauge did not register full, but only ~7/8th's full. After driving for a short while I noticed that the gauge went to ~ 3/4th's full. I stopped by my MB dealer to find out what was going on. Service rep told me that it probably had something to do with the fuel sender not having the same resistance as the system, and
that it would probably balance itself in a short time. I took an appointment to have the system checked by the technicians. The gauge did register full later in the day, but the next morning it at first registered 3/4, then shortly went to full, then back to 7/8th's. Car went into dealers on Friday and they were to check out the electrical system. They found out that one of the fuel sending units was defective (p/n 210-542-08-17) and it was replaced. This was covered by the warranty as the car has only 2,446 miles on it. I will keep a close eye on it - apparently it is OK now.